Field of the Invention
The present invention relates to a power supply device which supplies power to a load by utilizing a magnetic coupling between coils.
Description of the Related Art
As a method for supplying power to a load by utilizing a magnetic coupling between coils by electromagnetic induction, a non-contact power supply is given as an example. The principle thereof is forming a sort of a transformer by magnetically coupling a plurality of coils via a space, utilizing the electromagnetic induction between the coils, thereby exchanging power.
For example, the method includes arranging a primary side coil which corresponds to a power supply source as a power supply line in a rail shape, integrating a secondary side coil with a power receiving circuit to configure a mobile object, and at the same time, making the primary side coil and the secondary side coil be opposed to each other. With this, it is possible to conduct a non-contact power supply to a mobile object which moves along the power supply line.
Here, FIG. 41 illustrates a non-contact power supply device described in Japanese Laid-open Patent Publication No. 2002-354711. In FIG. 41, to both ends of a high-frequency power source 100, a primary side power supply line 110 is connected as a coil. To the primary side power supply line 110, a power receiving coil 120 is magnetically coupled, and the primary side power supply line 110 and the power receiving coil 120 form a sort of a transformer.
Both ends of the power receiving coil 120 are connected to a pair of AC (alternating-current) terminals of a full-wave rectifier circuit 10 through a resonance capacitor C. The power receiving coil 120 and the resonance capacitor C configure a series resonance circuits.
The full-wave rectifier circuit 10 is configured by bridge-connecting diodes Du, Dv, Dx, and Dy.
To a pair of DC (direct-current) terminals of the full-wave rectifier circuit 10, a constant voltage control circuit 20 is connected which controls a DC output voltage of the full-wave rectifier circuit 10 so that the DC output voltage is to be a reference voltage value. The constant voltage control circuit 20 is configured of a step-up chopper circuit which is formed, for example, of a reactor L1, a diode D1, a smoothing capacitor C0, and a semiconductor switch SW1. Further, to both ends of the smoothing capacitor C0, a load R is connected.
In FIG. 41, a control device for switching a semiconductor switch SW1 is omitted.
In the conventional technology disclosed in FIG. 41, a high-frequency current is applied to the primary side power supply line 110 by a high-frequency power source 100 and the high-frequency current supplied through the power receiving coil 120 is input into the full-wave rectifier circuit 10 to convert it into a direct current.
Generally, in this type of a non-contact power supply device, due to a change in a gap length between the primary side power supply line 110 and the power receiving coil 120, a change in a position gap of both, or the like, a voltage induced in the power receiving coil 120 changes. With this, the DC output voltage of the full-wave rectifier circuit 10 changes. Further, characteristics of the load R also cause the DC output voltage of the full-wave rectifier circuit 10 to change.
Accordingly, in the conventional technology disclosed in FIG. 41, the DC output voltage of the full-wave rectifier circuit 10 is controlled to have a constant value by the constant voltage control circuit 20.
In the non-contact power supply device, the higher the frequency of the current supplied through a coil is, the smaller excitation inductance necessary for transmitting a power may become, and a size of a coil or a core arranged at a periphery of the coil may be made to be small. However, in the power converter which configures a high frequency power device or a power receiving circuit, the higher the frequency of the current flowing through the circuit is, the larger an increase in a switching loss of a semiconductor switch becomes, and a power supply efficiency lowers. Accordingly, it is common to set the frequency of the power supplied in a non-contact state as several [kHz] to several tens of [kHz].
The non-contact power supply device disclosed in FIG. 41, and in particular, the power receiving circuit in a subsequent stage of the resonance capacitor C, has the following problems.
(1) Since a power receiving circuit is configured by a full-wave rectifier circuit 10 and a constant voltage control circuit 20, a size of an entire circuit becomes large and it causes an increase in installation space or cost.
(2) Since losses occur not only in diodes Du, Dv, Dx, and Dy of the full-wave rectifier circuit 10 but also in a reactor L1, a semiconductor switch SW1, and diode D1 of the constant voltage control circuit 20, these losses cause a reduction in a power supply efficiency.
In view of the above mentioned points, inventors have proposed a non-contact power supply device and a method for controlling the same (hereafter called a prior application invention) as described in Japanese Laid-open Patent Publication No. 2012-125138 (hereafter called a prior application). According to this, a small sized and inexpensive power supply device may be obtained and a highly efficient and stable power supply may become available.
FIG. 42 illustrates a first non-contact power supply device according to the above mentioned prior application.
In FIG. 42, 310 is a power receiving circuit. The power receiving circuit 310 includes bridge-connected semiconductor switches Qu, Qx, Qv, and Qy, diodes Du, Dx, Dv, and Dy, capacitors Cx and Cv, and a smoothing capacitor C0. Diodes Du, Dx, Dv, and Dy are connected in inverse parallel with each of the switches Qu, Qx, Qv, and Qy, respectively. Capacitors Cx and Cy are connected in parallel with each of the switches Qx and Qy of a lower arm, respectively. A smoothing capacitor C0 is connected between DC terminals of a bridge circuit (full-bridge inverter) being formed of these elements. A series circuit of a resonance capacitor C and a power receiving coil 120 are connected between AC terminals of a bridge circuit, and a load R is connected at both ends of a smoothing capacitor C0.
200 is a control device which generates a driving signal for switching semiconductor switches Qu, Qx, Qv, and Qy. The control device 200 generates the above mentioned driving signal on the basis of a current i of the power receiving coil 120 detected by a current detection unit CT and a DC output voltage (voltage between DC terminals) V0 of the power receiving circuit 310.
In the non-contact power supply device, by controlling semiconductor switches Qu, Qx, Qv, and Qy, an AC voltage v of a bridge circuit is controlled to a positive-negative voltage in which a DC output voltage V0 is set as a peak value. A power supplied from the primary side power supply line 110 to the power receiving circuit 310 is a product of a current i of a power receiving coil 120 and an AC voltage v of a bridge circuit. As the control device 200 adjusts a phase of driving signals of semiconductor switches Qu, Qx, Qv, and Qy on the basis of a DC output voltage V0, a control of the supplied power, that is, a constant control of a DC output voltage V0, becomes available.
Further, by configuring the power receiving circuit 310 using a bridge circuit which is formed of switches Qu, Qx, Qv, and Qy and diodes Du, Dx, Dv, and Dy, an operation of keeping the power constant is available even when a load R is a regenerative load.
According to this non-contact power supply device, a DC output voltage V0 may be controlled in a constant state by a phase control of driving signals of semiconductor switches Qu, Qx, Qv, and Qy without using a constant voltage control circuit as in the prior technology of FIG. 41. In addition, the power receiving circuit 310 may be configured only of abridge circuit and a smoothing capacitor C0. Therefore, a circuit configuration may be simplified, the size and the cost thereof may be reduced, and further, losses may be reduced by reducing the number of components, and consequently, a highly efficient and stable non-contact power supply may become available.
In addition, by a charging/discharging operation of capacitors Cx and Cv, a so-called soft-switching is made to be conducted to reduce switching losses, thereby allowing a further higher efficiency.
FIG. 43 illustrates a second non-contact power supply device according to the above mentioned prior application.
In the non-contact power supply device of FIG. 42, since four semiconductor switches are necessary, there is a concern that a size and a cost of the device will increase if considered a cooling unit. Therefore, the non-contact power supply device of FIG. 43 intends to further reduce the size and the cost by not corresponding to a regenerative load but by corresponding only to a power load.
In FIG. 43, the power receiving circuit 320 has a switching arm series circuit wherein an arm in which a diode Du is connected in inverse parallel with a semiconductor switch Qu and an arm in which a diode Dx is connected in inverse parallel with a semiconductor switch Qx are connected in series. Together with this, the power receiving circuit 320 has a diode series circuit in which diodes Dv and Dy are connected in series. These switching arm series circuit and diode series circuit are connected in parallel, and a smoothing capacitor C0 is connected at both ends of the diode series circuit. The configurations of components other than the power receiving circuit 320 are similar to those illustrated in FIG. 42.
FIG. 44 illustrates an explanatory view for an operation of a non-contact power supply device illustrated in FIG. 43.
In the non-contact power supply device of FIG. 43, the voltage v between AC terminals is controlled to a positive-negative voltage in which a DC output voltage V0 is set as a peak value, by controlling semiconductor switches Qu and Qx. A power supplied from the primary side power supply line 110 to the power receiving circuit 320 is a product of a current i and a voltage v in FIG. 44. Accordingly, as the control device 200 adjusts a phase of driving signals of semiconductor switches Qu and Qx on the basis of a DC output voltage V0, a control of the supplied power, that is, a constant control of a DC output voltage V0, becomes available.
According to the non-contact power supply device of FIG. 43, since semiconductor switches for two out of four elements which configure a bridge circuit become unnecessary, a switching loss may be reduced to a large extent. Together with this, a size of a cooling fin for the bridge circuit may be reduced, and thereby be capable of further reducing the size and cost of an entire device.
Therefore, according to the invention of the prior application, compared with prior technology related to Japanese Laid-open Patent Publication No. 2002-354711, a loss may be reduced to a large extent, and a size and cost of the device may be reduced as well.
However, according to the prior application invention, as illustrated in FIG. 44, a current i becomes a leading phase to a fundamental wave component v′. Therefore, a problem of a reduced power factor of the non-contact power supply device occurs and the problem invites an increase in a loss in the entire device and causes obstructions in further reducing the size of the entire device.